The principal investigator has previously studied the immunosuppressive effects of hamster serum fraction enriched for alpha2 macroglobulin (alpha 2M). In these studies these was a differential inhibition of stimulation of lymphocytes by B cell mitogens. The inhibitory fraction (alpha 2M) also possessed protease inhibitor activity. The purpose of this study is to extend the biochemical purification of alpha 2M and analyze its biological role as a regulator of cellular proliferation. Initial experiments will be directed toward biochemical isolation and characterization of alpha 2M from hamster serum as well as characterization of a monospecific antisera generated in rabbits. The following biological characteristics of alpha 2M from serum will be investigated: (1) The role of alpha 2M in proliferation will be analyzed by adding alpha 2M serum fractions to short term primary antibody forming cell culture; (2) cells bearing suface alpha 2M will be localized and distribution patterns followed by utilization immunofluorescent antibody techniques. Radiolabelled alpha 2M may identify subpopulations of cells which bind alpha 2M. (3) Various cell populations will be cultured in the presence of radiolabelled amino acids to permit identification (immunoprecipitation) of cells which synthesize alpha 2M. (4) Serum alpha 2M levels of normal and immunized animals will be quantitated by radioimmunoassays. Once the biological characteristics are determined for normal animals and normal cells, the investigation will be extended to study the same qualities in tumor bearing animals and in vitro transformed cell lines. The results obtained from the proposed research will provide information on how protease/protease inhibitor systems may aid in regulation of cellular proliferation and/or differentiation and more specifically how the interaction of tumor cells and the immune system may result in immunosuppression through these molecules.